Copolymers of organopolysiloxane with various materials have been described previously. For example, block copolymers of organopolysiloxane and resins such as polystyrene have been described in U.S. Pat. Nos. 3,051,684; 3,483,270; 3,760,030; and 4,677,169. Block copolymers of silicones with vinyl pyridine have been described in U.S. Pat. Nos. 3,673,272 and 3,875,254. Block polymers of polysiloxanes and dienes such as polybutadienes are described in U.S. Pat. No. 3,928,490. The '490 block polymers are prepared by joining linear high molecular weight polysiloxane and a butadienyl dilithium initiator or catalyst in a solvent to form the desired linear block copolymer. In U.S. Pat. Nos. 3,051,684 and 3,483,270, cyclic tri- and tetrasiloxanes are described as reactive with diene or vinyl monomers to form block copolymers containing siloxane and polydiene or polyvinyl blocks, respectively.
A clean and facile release of manufactured rubber articles and process goods from the flexible machinery components contacted during the manufacturing process is a critical feature of such processes. The undesirable adhesion of such articles and goods to the machinery components may result in unnecessary delays in the production schedule and/or damaged goods due to the force required to separate the goods from the machinery components when the process is completed.
The problem of releasing manufactured rubber articles from machinery components is particularly prevalent with elastomeric and flexible structures or components such as conveyor belts and devices such as flexible diaphragms, bags, bladders, sleeves, etc. which are often made of elastomeric materials such as rubber which possess a natural stickiness or tack. It is desirable, therefore, to provide elastomeric materials having both controlled surface release characteristics and elastomeric flexible properties, i.e., flexible surfaces with reduced tack or stickiness.
Many of the suggestions which have been made in the prior art for providing a convenient, safe and economical means for controlling the natural surface tack or stickiness of flexible elastomeric structures and machinery components generally involve depositing a release coating on the flexible surface which contacts the articles or goods. Various materials have been suggested in the art as release materials of films, and these include, for example, mica, polymeric polyols, cellulose ethers, clay such as bentonite, and silicone lubricants. Such release materials are generally applied to the elastomeric material by painting, dusting, dipping or spraying of the article.
U.S. Pat. No. 4,853,069 describes an elastomeric structure wherein the release characteristics are controlled with a surface coating comprising a chloro-sulfonated polymer and a reinforcing filler. An aqueous emulsion useful as a lubricant for tire-curing bladders is described in U.S. Pat. No. 4,533,305. The lubricant composition comprises a mixture of polydimethylsiloxane; at least one silane selected from methyl hydrogen silane, dimethyl hydrogen silane and methyl trimethoxy silane; a surfactant; water; and optionally, a metal salt of an organic acid.
Machines for the assembly (forming) of tires (TAMS) contain elastomeric structures such as inflatable rubber bladders which are conventionally used for such manufacturing operations as turning up ply ends over bead rings and against plies on the TAM mandrel or drum. These rolling, inflatable turn-up bladders (TUBS) turn the ends of the plies wrapped on the tire building mandrel up around the bead rings and over them against the ply material. The rubber ply material of the tire stock is tacky by nature, and it is this tack which causes the plies to stick together and thus maintain the integrity of the partially built or green tire. The TUBS are conventionally made from vulcanized rubber with optional fabric reinforcement, and the tacky ply ends of the tire stock have a tendency to adhere to the outer surface of the bladder which turns them up, particularly, since the inflated bladder exerts pressure on the turned-up ply ends. This adhesion tends to retard the subsequent retraction of the deflated bladders, and it can also result in erosion of the bladder material coming in contact with the ply ends. Thus it is desirable to provide TUBS with surfaces which are non-adhesive or releasing to the tire plies with which they may come in contact. One solution to this problem is found in U.S. Pat. No. 4,381,331 to Johnson, which describes a ply turnover bladder having at least a portion of its outer surface comprising a fabric layer of spaced cords calendered with a coating of unvulcanized, uncured rubbery polymer, the spaces between the cords being free of said polymer at the surface so that the cords project above said surface. It has been found that this structure has reduced tendency to adhere to the rubber ply of tire components and thus release the tire during its manufacture.
Another related embodiment of this invention is found in tire curing bladders having an outer releasing surface coating and in a method of curing tires utilizing such coated bladders. Conventionally, pneumatic rubber vehicle tires are produced by molding and curing a green or uncured and unshaped tire in a molding press. In the press, the green tire is pressed outwardly against the mold surface by means of an inner, fluid-expandable bladder. By this means the green tire is shaped against the outer mold surface which defines the tires tread pattern and configuration of the sidewalls. Generally the bladder is expanded by internal pressure provided by a fluid such as hot gas, hot water, and/or steam. The use of such tire curing bladders is well known in the art of tire manufacture. It is also known that difficulties may occur between the bladder and the inner surface of the tire if there is excessive adhesion, that is, the lack of release between the two. Typically, this results in deterioration of the bladder, misshaping of the tire in the mold, and similar problems. Furthermore, air bubbles can potentially become trapped between the bladder and tire surfaces and promote tire vulcanization defects. For this reason, it is conventional practice to precoat the inner surface of the green or uncured tire with a lubricant in order to provide lubricity between the outer bladder surface and the inner tire surface. Such lubricants have sometimes been called lining cements, band ply dopes and bag dopes. Conventionally, the inner surface of the green tire, which is typically a rubber gum stock, is simply spray coated with a lubricant which might, for example, be based on silicone polymers. Other additives may also be conventionally utilized in this application, such as mica, polymeric materials, polyols, polyethers, clays, and the like. Another approach to this problem is the alternative of coating the bladder itself. One such example of a tire curing bladder lubricant is found in U.S. Pat. Nos. 4,359,340 and 4,533,305, both to Comper et al, which describe an aqueous lubricating composition for tire curing bladders containing polydtmethylsiloxane, a silane, a surfactant and, optionally, a metal salt of an organic acid.
Still another means of solving the problem of undesirable adhesion between tacky tire plies and similar elements and flexible TAM components such as bladders and sleeves is the so-called Red Release coat developed by The Firestone Tire & Rubber Company. This coat consists of a polymeric film formed from a fluxed (that is, heat-treated) blend of PVC and a copolymer of butadiene and acrylonitrile (for example, Paracril OZO). This material is available as a thin sheet that is cemented to the bladder or sleeve on which the release coating is desired.